Matrimid hollow fibers, originally developed for standard gas separation, were adapted to dehydrate acetic acid (HAc) and water mixtures in this work. These fibers, with an integrally defect-free skin layer supported on an open porous substrate, exhibit intrinsic selectivity for gases such as N-2, O-2, and He. When applied to separate HAc and water mixtures, the separation factor and water flux of similar to 15 and 2.5 kg/m(2) h, respectively, were obtained for a regular 250 mu m outer diameter and 20 cm long defect-free hollow fiber in a pervaporation process at 101.5 degrees C. A large bore pressure change along the axial direction of hollow fibers was shown to be negatively impacting separator performance. The separation factor and water flux were, therefore, increased by similar to 150% using a similar fiber with a diameter twice as large as that of the regular gas separation fiber.